Polymers

ABSTRACT

Described herein are polymers and associated methods to occlude structures and malformations of the vasculature with polymers with delayed controlled rates of expansion. Methods of forming such devices are also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 15/179,212, filed Jun. 10, 2016, which claims the benefit of U.S. provisional patent application No. 62/174,425, filed Jun. 11, 2015, the entire disclosure of each of which are incorporated herein by reference.

FIELD

The present invention relates generally to expansile polymers and medical treatment methods using the polymers.

SUMMARY

Described herein generally are expansile polymers such as hydrogels. The polymers can be formed as filaments. Methods of forming these polymers are also described. Further, medical treatment methods using the polymers are described. In some embodiments, when formed as a filament, the filaments described herein possess enough structural strength to not require support members. In other embodiments, the hydrogel filaments require support members. The filaments can also be opacified in order to visualize the filaments using medically relevant imaging techniques.

In one embodiment described herein are expansile devices for implantation in an animal, such as a mammal, such as a human. The expansile devices can comprise an expansile polymer including a reaction product of a polymerization solution including a macromer, a monomer, a first crosslinker, and a second crosslinker. In some embodiments, the second crosslinker is cleavable. In some embodiments, the second cleavable crosslinker imparts a secondary expansion to the expansile polymer.

The expansile devices can include at least one visualization element, which can be metallic powders, gadolinium, superparamagnetic iron oxide particles, barium sulfate, or a combination thereof. In one embodiment, the at least one visualization element is barium sulfate.

The monomer used in the herein described polymers can be pH sensitive and provide a first expansion to the expansile polymer. In other embodiments, the monomer may not be pH sensitive. In other embodiments, a monomer may not be used. In some embodiments, a macromer may be pH sensitive and/or provide expansion characteristics to the polymer. In some embodiments, the macromers and the monomers may have expansion characteristics.

In some embodiments, the first crosslinker can be N,N′-methylenebisacrylamide.

The second cleavable crosslinker can be an acrylate based crosslinker such as a methacrylate based crosslinker. In some embodiments, the second cleavable crosslinker can be an acrylic anhydride based crosslinker. The acrylic anhydride can be a methacrylate based anhydride crosslinker and can have a structure

wherein n is 0, 1, 2, 3, 4, or 5. Further, the acrylic anhydride based crosslinker can be synthesized by reaction of a di-acid with methacrylic anhydride.

Methods of forming expansile polymers are also described. Methods can comprise polymerizing a polymer from a polymerization solution comprising a macromer, a monomer, a first crosslinker, and a second cleavable crosslinker. The methods can further include a step of treating said polymer in a non-physiological pH for a predetermined amount of time thereby creating an environmentally responsive hydrogel.

In some embodiments, the non-physiological pH that the polymers are treated in can be basic. In other embodiments, the non-physiological pH can be acidic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts Scheme 2 showing a cleavable second type of crosslinker included in the hydrogel structure or matrix.

DETAILED DESCRIPTION

Described herein generally are expansile polymers such as hydrogels. The polymers can be formed into virtually any shape or form. In one embodiment, the polymers can be formed as filaments or other elongated structures. The polymers can have tuned rates of expansion and can incorporate a secondary expansion mechanism by including a crosslinker that can cleave upon a particular physiological event and allow expansion to what the polymer would normally expand to without the cleavable crosslinker. In other words, cleavable crosslinks can prevent full expansion or retard expansion until a cleavable event occurs and the polymer can fully expand.

Methods of forming the polymers are also described herein, including methods of making the polymers environmentally responsive and expandable at a predetermined rate for a predetermined amount of time. This expansion rate can be tailored using at least the secondary expansion mechanism by incorporation of a second cleavable crosslinker. Polymer expansion can be further tailored by including different types of cleavable crosslinkers such as a third, fourth, fifth or subsequent cleavable crosslinkers. In other embodiments, expansion can be tailored by using a different density or concentration of cleavable crosslinkers.

The expansile polymers and associated methods are for occluding structures and malformations resulting from one or more cerebral and/or peripheral vascular diseases. The polymers can have delayed and/or controlled rates of expansion. These controlled rates of expansion give surgeons a sufficient amount of time to deliver the polymer through a microcatheter or catheter filled with blood or saline at physiological pH without the need to rush as a result of immediate expansion. For use with a catheter, a polymer filament may be desired. Further, the polymers can include one or more visualization agents, for example, radiopaque elements or fillers to allow visualization during implantation.

Generally, the polymers, e.g., hydrogel filaments, can be deployed within the vasculature using standard practices and microcatheters/catheters to occlude blood flow.

As used herein, the term “environmentally responsive” refers to a material (e.g., a hydrogel or polymer described herein) that is sensitive to changes in environment including but not limited to pH, temperature, and pressure. Many of the expansile materials described herein are environmentally responsive at physiological conditions.

As used herein, the term “non-resorbable” refers to a material (e.g., a hydrogel) that cannot be readily and/or substantially degraded and/or absorbed by bodily tissues.

As used herein, the term “unexpanded” refers to the state at which a hydrogel is substantially not hydrated and, therefore, not expanded. In some embodiments described herein, a hydrogel filament is generally unexpanded prior to implantation into a patient.

As used herein, the term “ethylenically unsaturated” refers to a chemical entity (e.g., a macromer, monomer or polymer) containing at least one carbon-carbon double bond.

In some embodiments, when formed as a filament or other elongated structure, the filaments described herein may not have support members, such as no metal or metallic support members, to aid in supporting the filaments before, during and after implantation. When formed as a filament or other elongated structure, the filaments can possess enough structural column strength to not require support members.

The polymers described when provided as filaments or other elongated structures can have round, square, rectangular, triangular, pentagonal, hexagonal, heptagonal, octagonal, ellipsoidal, rhomboidal, torx, or star-shaped cross-sectional shapes. A filament can be described as having a three dimensional shape such as, but not limited to a thread, string, hair, cylinder, fiber, or the like. The filament can be elongated meaning that its length exceeds its width or diameter by at least 5, 10, 15, 20, 50, 100, 500, 1,000 or more times.

The filaments can be delivered through a catheter or microcatheter using a liquid flush (e.g. saline). The filaments have sufficient column strength to alleviate the need for a metal support member, yet soft and flexible enough to navigate through vasculature. However, in some embodiments, the filaments described herein do not have sufficient column strength to be advanced out of a catheter device by pushing with a metal wire. Here, as described above, a liquid flush, in some cases a pressurized liquid flush, can be used to advance the filaments through and out of a catheter or microcatheter.

The polymers described herein can be formed from polymerization solutions or prepolymer solutions comprising such components as one or more solvent(s), one or more macromer(s), one or more monomer(s), one or more cross-linker(s), one or more visualization agent(s), and one or more initiator(s). Some components are optional. In one embodiment, the hydrogel filaments can include a polymer which can be a reaction product of (i) one or more macromers, (ii) one or more monomers, and/or (iii) two or more different crosslinkers, wherein one of the crosslinkers is a cleavable crosslinker. The polymers can also optionally include one or more pharmaceutical agents. The polymers can also include one or more visualization agents.

A particular combination of monomers/macromers/crosslinkers can provide differing polymeric physical properties. Different polymeric physical properties can include, but are not limited to tensile strength, elasticity, and/or delivery through a microcatheter or catheter.

The solvent's function in the polymerization solution is complete dissolution of all macromers, monomers, cross-linkers, initiators, and/or soluble visualization agents needed to form a particular filament. In other embodiments, the solvent can dissolve substantially all of the macromers, monomers, cross-linkers, initiators, and/or soluble visualization agents needed to form a particular filament. In some embodiments, the visualization agent or agents do not dissolve in the solvent.

If a liquid monomer (e.g. 2-hydroxyethyl methacrylate) is used, a solvent may not be necessary. The solvent, if necessary, is selected based on the solubility of the components of the polymerization solution. Solvents can include isopropanol, ethanol, water, dichloromethane, and acetone. However, any number of solvents can be utilized and a skilled artisan can match a solvent to a particular polymer system.

Solvent concentrations can range from about 20% w/w to about 80% w/w of the polymerization solution. In other embodiments, the solvent ranges from about 40% w/w to about 60% w/w or about 30% w/w to about 50% w/w. In one embodiment, the solvent makes up about 40% w/w of the polymerization solution.

Macromers described herein can include large molecular weight compounds such as polymers having one or more reactive groups. In some embodiments, macromers with solubility in solvents and functional groups amenable to modifications may be used. Polyethers, due to their solubility in a variety of solvents, their availability in a variety of forms, and their available hydroxyl groups, may be used as macromers. Other macromers can include, but are not limited to, poly(ethylene glycol), poly(propylene glycol), and poly(tetramethylene oxide).

In other embodiments, a low molecular weight macromer can be used and/or in other embodiments, a branched macromer may be used. A low molecular weight, branched macromer can include at least three reactive moieties per molecule so that a high crosslink density of the finalized polymer can be achieved. Example low molecular weight, branched macromers can include ethoxylated pentaerythritol having four end groups per molecule, and ethoxylated trimethylolpropane having three end groups per molecule.

In still other embodiments, non-polyether polymers with functional groups available for modification, such as poly(vinyl alcohol), can also be used as macromers.

Macromers can be present at a concentration of about 10% w/w, about 15% w/w, about 20% w/w, about 25% w/w, about 30% w/w, about 35% w/w, about 40% w/w, about 45% w/w, about 50% w/w, at least about 10% w/w, between about 10% w/w and about 40% w/w, between about 15% w/w and about 25% w/w, between about 15% w/w and about 50% w/w, or between about 15% w/w and about 30% w/w, of the polymerization solution. In one embodiment, the macromer concentration is about 15% w/w of the polymerization solution.

The molecular weight of the macromer can alter the mechanical properties of the resulting polymer or hydrogel filament. In some embodiments, the alteration of the mechanical properties can be substantial. Smaller molecular weights result in polymers with sufficient column strength to be pushed through microcatheters and catheters when formed as a filament or other elongated structures. Larger molecular weights can result in polymer filaments that can be pushed through microcatheters and catheters with more difficulty. As such, the macromers described herein can have a molecular weight of about 50 g/mole, about 100 g/mole, about 200 g/mole, about 300 g/mole, about 400 g/mole, about 500 g/mole, about 1,000 g/mole, about 1,500 g/mole, about 2,000 g/mole, about 2,500 g/mole, about 3,000 g/mole, about 3,500 g/mole, about 4,000 g/mole, about 4,500 g/mole, about 5,000 g/mole, at least about 50 g/mole, at least about 100 g/mole, between about 50 g/mole and about 5,000 g/mole, between about 100 g/mole and about 5,000 g/mole, between about 1,000 g/mole and about 5,000 g/mole, between about 100 g/mole and about 1,000 g/mole, or between about 500 g/mole and about 1,000 g/mole. In one embodiment, the molecular weight is between about 500 g/mole to about 1,500 g/mole.

The polymerization solutions can include at least one macromer. The macromer can be of low molecular weight, shapeable, multifunctional (e.g. difunctional), ethylenically unsaturated or a combination thereof. At least one of the macromer's roles is to impart the desired mechanical properties and/or structural framework to the herein described polymers. In general, any polymer can function as a macromer. However, polymers with solubility in solvents and functional groups amenable to modifications can also be used. Polyethers, due to their solubility in a variety of solvents, their availability in a variety of forms, and their available hydroxyl groups, can be used. Poly(ethylene glycol), poly(propylene glycol), ethoxylated trimethylol propane, and poly(tetramethylene oxide) can all be suitable for use herein. In another embodiment, a macromer can be poly(ethylene glycol). Poly(ethylene glycol) is preferred because of its solubility in aqueous solutions. Likewise, cross-linked networks of poly(ethylene glycol) swell in aqueous solutions. Non-polyether polymers with functional groups available for modification, such as poly(vinyl alcohol), can also be utilized as macromers. Macromer concentrations can range from about 5% w/w to about 50% w/w, about 10% w/w to about 40% w/w, about 15% w/w to about 30% w/w, or about 16% w/w to about 29% w/w of the polymerization solution. In one embodiment, the macromer concentration is about 19% w/w, about 25% w/w or about 29% w/w of the polymerization solution.

In some embodiments, the macromer is shapeable. Shapeability describes the macromer's relative rigidity and its ability to hold a particular shape. For example, a shapeable macromer according to the present description can be formed using a device such as a mandrel and can hold the resulting shape for implantation.

The molecular weight of the macromer can dramatically change the resulting polymer's mechanical properties. Smaller molecular weights result in polymers when formed as filaments that have sufficient column strength to be pushed through microcatheters and catheters. Larger molecular weights result in polymers that when formed as filaments, can require more effort to be pushed through microcatheters and catheters.

The macromers described herein have a molecular weight ranging from about 100 g/mole to about 100,000 g/mole or about 500 g/mole to about 50,000 g/mole. In one embodiment, molecular weight ranges from about 5,000 g/mole to about 15,000 g/mole. In another embodiment, the molecular weight is about 10,000 g/mole. One embodiment includes poly(ethylene glycol) diacrylamide with a molecular weight of about 10,000 g/mole.

Any functional groups associated with the macromers described can be derivatized. The functional groups of the macromers can be derivatized to impart ethylenically unsaturated moieties allowing free radical polymerization of the hydrogel. Functionalities for free radical polymerization can include acrylates, methacrylates, acrylamides, vinyl groups, and derivatives thereof. Alternatively, other reactive chemistries can be employed to polymerize the hydrogel, for example, nucleophile/N-hydroxysuccinimde esters, nucleophile/halide, vinyl sulfone or maleimide. In one embodiment, a functional group of the macromer is an acrylate.

Biostability (or non restorability) or biodegradation can be imparted to polymers described by altering the synthetic route to derivatize macromer functional groups. If biostability is desired, linkage stability in the physiological environment can be utilized. In one embodiment, a biostable linkage is an amide. The macromer hydroxyl group(s) is converted to an amino group followed by reaction with acryloyl chloride to form an acrylamide group. If biodegradation is desired, linkages susceptible to breakage in a physiological environment can be utilized. In some embodiments, biodegradable linkages can include esters, polyesters, and amino acid sequences degradable by enzymes.

Monomers used to form the herein described polymers can have low molecular weights and/or can contain a single polymerizable group. If present, the monomer(s) can aid in polymerization and impart specific mechanical properties to the resulting polymer. The monomers can be any molecule with a single functionality and conducive to a desired mechanical property.

Specific monomers can include, but are not limited to, t-butyl acrylamide, 2-hydroxyethyl methacrylate, hydroxyl propyl acrylate, hydroxyl butylacrylate, and derivatives thereof. The hydrophobicity and bulky structure of these specific monomers can impart column strength to the resulting polymer.

In some embodiments, a visualization agent can be a monomer and incorporated into the polymeric structure.

Monomers, if present, can be present at a concentration of about 5% w/w, about 10% w/w, about 15% w/w, about 20% w/w, about 25% w/w, about 30% w/w, about 35% w/w, about 40% w/w, about 45% w/w, about 50% w/w, at least about 5% w/w, between about 5% w/w and about 40% w/w, between about 10% w/w and about 50% w/w, between about 5% w/w and about 30% w/w, or between about 5% w/w and about 20% w/w, of the prepolymer solution.

Monomers sensitive to pH can be utilized in the polymers described herein thereby imparting environmental sensitivity to them. The main function of the pH sensitive monomer is to permit control over the polymer's rate of expansion. Such monomers must include functionality allowing incorporation into the resulting polymer during polymerization and ionizable moieties, for example, carboxylic acids or amines. Concentrations of pH sensitive monomers in the polymerization solution can range from about 1% to about 12.5%. In some embodiments, pH sensitive monomers can be acrylic acid, methacrylic acid, amino methacrylate, amino methacrylamide, and derivatives and salts thereof. In some embodiments, pH sensitive monomers are not utilized.

Generally, the controlled rate of expansion of the polymers is imparted through the incorporation of ethylenically unsaturated monomers with ionizable functional groups, (e.g. acidic or basic groups). For example, if acrylic acid is incorporated into the cross-linked polymeric network, it can be introduced through a microcatheter filled with blood or saline at physiological pH. The polymer cannot and may not expand until the carboxylic acid groups deprotonate. Conversely, if a basic, amine containing monomer is incorporated into the cross-linked network, the polymer can be introduced through a microcatheter filled with blood or saline at physiological pH. The polymer cannot and will not fully expand until the amine groups are protonated.

In one embodiment, pH-sensitive monomers are incorporated into the polymers to control the rate of expansion to permit delivery through microcatheters and catheters filled with physiological fluids. In one embodiment, ethylenically unsaturated carboxylic acids are incorporated into the polymers. In another embodiment, salts of ethylenically unsaturated carboxylic acids are incorporated into the polymers and subsequently the polymers are incubated in a low pH solution to protonate all the salts of the carboxylic acids. Expansion occurs in a physiological environment as the carboxylic acids deprotonate. In another embodiment, salts of ethylenically unsaturated amines are incorporated into the polymers and subsequently the polymers are incubated in a high pH solution to deprotonate the salts of the amines. Expansion occurs in a physiological environment as the amines protonate. In yet another environment, pH sensitive monomers are not incorporated into the polymers.

Non-pH sensitive monomers can also be used to aid in polymerization of the polymers and impart specific mechanical properties to the polymers. The non-pH sensitive monomers can be any molecule with a single functionality to incorporate into the polymers and/or a structure conducive to the desired mechanical property. The non-pH sensitive monomers can be, for example, hydrophobic thereby imparting column strength to the polymers. Also or in addition, the non-pH sensitive polymers can have a bulky structure further imparting column strength. Internal hydrogen bonding within the non-pH sensitive monomer imparts increasing tensile strength. In some embodiments, non-pH sensitive monomers can be t-butyl acrylamide, 2-hydroxyethyl methacrylate, and derivatives thereof. Concentrations of non-pH sensitive monomers can range from about 0% to about 20% w/w, about 15% w/w, about 12% w/w or about 11% w/w of the polymerization solution.

In one embodiment, depending on the monomers chosen for a particular polymer, significant fluid uptake by the polymer can occur and a large increase in the volume of the polymer can occur in a physiological environment. In another embodiment, monomers chosen allow only a small amount of fluid uptake by the polymer and only a small increase in the volume of the polymer occurs in a physiological environment. In yet another environment, monomers chosen prevent fluid uptake by the polymer and the volume of the polymer remains unchanged in a physiological environment.

Crosslinkers can also be utilized to impart cross-linking of the resulting polymer. A crosslinker can be any molecule with at least two functionalities to incorporate into the resulting polymer. The crosslinker can also be a structure conducive to the desired mechanical property imparted on the finalized polymer.

Crosslinkers can include an ester, a carbonate, a thioester, an anhydride, or a combination thereof. In other embodiments, multiples of each of an ester, a carbonate, anhydrides, and/or a thioester can be included. In one embodiment, a crosslinker can be an anhydride.

Other crosslinkers can include N,N-methylenebisacrylamide and ethylene glycol dimethacrylate.

Cross-linker(s), when used in the described polymers, impart desired mechanical properties. The cross-linker can be any molecule with at least two functionalities to incorporate into the polymers and preferably a structure conducive to the desired mechanical property. In one embodiment, a cross-linker is N,N-methylenebisacrylamide. Concentrations of the cross-linker can be less than about 1% w/w, less than about 0.8% w/w, less than about 0.5% w/w, or less than about 0.1% w/w of the polymerization solution. In one embodiment, the concentration of cross-linker is about 1% w/w.

A second type of crosslinker can also be included in the final polymer. The second type of crosslinker can impart a secondary mechanism of expansion to the hydrogel filaments. This secondary mechanism can be one that increases the swelling size of the hydrogel, but does not impact the initial rate of swelling. In some embodiments, the second type of crosslinker can retard full expansion of the polymer until the crosslinker is cleaved.

Possibilities for a second type of crosslinker can include crosslinkers that can be cleaved or degraded. For example, cleavable linkages include esters, polyesters, and amino acid sequences degradable by enzymes. In other embodiments, the second type of crosslinker can include hydrolyzable moieties such as anhydrides. Anhydrides will begin to cleave as the hydrogel hydrates. However, in some embodiments, the cleavage rate may be slower than that of the initial expansion of the hydrogel resulting from hydration.

Cleavable crosslinkers can include acrylate based crosslinkers such as acrylic anhydride based crosslinkers. These crosslinkers can be synthesized by reaction of a di-acid with methacrylic anhydride. An example synthetic scheme (Scheme 1) is

wherein n is 0, 1, 2, 3, 4, or 5.

In some embodiments, the di-acid crosslinker can include ethylene, ethylene glycol, or propylene glycol repeating units to modulate the water solubility and the rate of degradation.

In some embodiments, when an anhydride based crosslinker is used, a resulting polymer can be sensitive to water. Thus, in some embodiments, gelation and purification of the resulting polymer can be performed in the absence of water.

In one embodiment, a first type of crosslinker and a second type of crosslinker can be used in the herein described hydrogels and polymers. In one embodiment, the second crosslinker can be a cleavable crosslinker. For example, as illustrated FIG. 1 in Scheme 2, a cleavable second type of crosslinker is included in the hydrogel structure or matrix.

The second type of crosslinker can incorporate secondary covalent cleavable crosslinks, in addition to a first type of permanent crosslinks, into the backbone. As these secondary covalent cleavable crosslinks are broken the polymer or hydrogel can expand to a larger diameter than the hydrogel would expand without the secondary crosslinkers present. In other words, hydrogels incorporating a second cleavable crosslinker in addition to a first permanent crosslinker can have a first expanded diameter when the hydrogel is swollen and a second, larger diameter when the cleavable crosslinks are broken or cleaved.

In effect, the hydrogel can initially expand to the extents limited by the initial crosslink density imparted by the cleavable crosslinks (e.g., the first diameter), and then subsequent hydrolysis of the cleavable crosslinks can allow the hydrogel to expand to a greater size (e.g., the second diameter).

In further embodiments, a third, fourth, fifth or more different cleavable crosslinkers can be included in a polymer or hydrogel described. Each cleavable crosslinker can have a different length and different degradation time to allow multiple steps of expansion before a final expansion size is achieved.

In some embodiments, the concentration of the second, cleavable type of crosslinker can be about 5% w/w, about 4% w/w, about 3% w/w, about 2% w/w, about 1% w/w, about 0.5% w/w between about 5% w/w and about 1% w/w, between about 2% w/w and about 0.5% w/w, or between about 5% w/w and about 0.5% w/w of the polymerization solution.

The concentration of all the crosslinkers in a polymerization solution can be less than about 10% w/w, less than about 5% w/w, less than about 4% w/w, less than about 3% w/w, less than about 2% w/w, less than about 1% w/w, or less than about 0.5% w/w of the polymerization solution.

In one embodiment, polymerization of the herein described polymers can be initiated using an initiator. An initiator can be azobisisobutyronitrile (AIBN) or a water soluble AIBN derivative. Other initiators useful according to the present description include N,N,N′,N′-tetramethylethylenediamine, ammonium persulfate, benzoyl peroxides, 2,2′-azobis(2-methylpropionamidine)dihydrochloride, and combinations thereof, including azobisisobutyronitriles. The polymerization solution can be polymerized by reduction-oxidation, radiation, heat, or any other method known in the art. Radiation cross-linking of the polymerization solution can be achieved with ultraviolet light or visible light with suitable initiators or ionizing radiation (for example, electron beam or gamma ray) without initiators. Cross-linking can be achieved by application of heat, either by conventionally heating the solution using a heat source such as a heating well, or by application of infrared light to the polymerization solution.

When used in the polymerization solutions described herein, an initiator starts the polymerization of the polymerization solution components. An exemplary initiator includes 2,2′-azobis(2-methylpropionamidine)dihydrochloride. Concentrations of the initiator can be less than about 1% w/w or less than about 0.5% w/w of the polymerization solution.

Visualization agents can also be added to the polymers described herein since metallic support members may not be used in conjunction with the presently described polymers. Generally, in the art, metallic support members aid in the visualization of embolic devices. Here, this may not be the case. The visualization agents impart visibility of the resulting polymers when imaged using a medically relevant imaging technique such as fluoroscopy, computed tomography, or magnetic resonance techniques.

Visualization of the polymers under fluoroscopy can be imparted by the incorporation of solid particles of radiopaque materials such as barium, bismuth, tantalum, platinum, gold, and other heavy nuclei species into the polymers or by the incorporation of iodine molecules polymerized into the polymer structure. In one embodiment, a visualization agent for fluoroscopy can be barium sulfate. Visualization of the polymers under computed tomography imaging can be imparted by incorporation of solid particles of barium or bismuth. Metals visible under fluoroscopy generally result in beam hardening artifacts that preclude the usefulness of computed tomography imaging for medical purposes. In one embodiment, a visualization agent for fluoroscopy can be barium sulfate. Concentrations of barium sulfate rendering the hydrogel filaments visible using fluoroscopic and computed tomography imaging can range from about 30% w/w to about 60% w/w, about 35% w/w to about 50% w/w, or about 39% w/w to about 47% w/w of the polymerization solution.

Visualization of the polymers under magnetic resonance imaging can be imparted by the incorporation of solid particles of superparamagnetic iron oxide or gadolinium molecules polymerized into the polymer structure. In one embodiment, a visualization agent for magnetic resonance is superparamagnetic iron oxide with a particle size of 10 microns. Concentrations of superparamagnetic iron oxide particles to render the polymers visible using magnetic resonance imaging can range from about 0.01% w/w to about 1% w/w, about 0.05% w/w to about 0.5% w/w, or about 0.1% w/w to about 0.6% w/w of the polymerization solution.

In one embodiment, a polymer can be formed from a reaction product of a difunctional, low molecular weight, ethylenically unsaturated, shapeable macromer, an ethylenically unsaturated monomer, a visualization element, a cross-linker, a second cleavable crosslinker that retards expansion of the polymer, and an initiator.

In another embodiment, a polymer can include a difunctional, low molecular weight, ethylenically unsaturated, shapeable macromer, an ethylenically unsaturated monomer, a visualization element, a cross-linker, and a second cleavable crosslinker that retards expansion of the polymer.

The polymers can have many characteristic properties one of which is bending resistance. The polymers when formed as filaments or other elongated structures can generally have a dry bending resistance of about 20 mg to about 200 mg, about 20 mg to about 32 mg or about 100 mg to about 200 mg. In the wet state, the bending resistance lowers drastically to about 2 mg to about 50 mg, about 2 mg to about 5 mg, or about 25 mg to about 50 mg.

Another characteristic is average ultimate tensile strength of the polymers when formed as filaments or other elongated structures. The filaments described herein have an average ultimate tensile strength of about 0.18 lbf to about 0.65 lbf, about 0.18 lbf to about 0.25 lbf, or about 0.52 lbf to about 0.65 lbf.

Methods of preparing the polymers is also described. The polymerization solution is prepared by dissolving the macromer, pH sensitive monomers, non-pH sensitive monomers, cross-linker, cleavable crosslinker, initiator, and soluble visualization agents in the solvent. After dissolution of these components, an insoluble visualization agent can be suspended in the polymerization solution. Mixing of the polymerization solution containing an insoluble visualization agent with a homogenizer aids in suspension of the insoluble visualization agent. The polymerization solution can then be polymerized to provide a polymer. The polymer can be dried.

In some embodiments, to form a filament, before polymerization, the polymerization solution can be injected into tubing with an inner diameter ranging from about 0.001 inches to about 0.075 inches and incubated for several hours in boiling water, for example, at 100° C., and subsequently overnight at 80° C. to complete the polymerization. The immersion in boiling water allows for rapid heat transfer from the water to the polymerization solution contained in the tubing. The selection of the tubing imparts microcatheter or catheter compatibility. For delivery through microcatheters, tubing diameters can range from about 0.006 inches to about 0.025 inches. For delivery through 4 and 5 Fr catheters, tubing can have diameters from about 0.026 inches to about 0.045 inches. In one embodiment, the tubing is made from HYTREL® (DuPont, Wilmington, Del.). The HYTREL® tubing can be dissolved in solvents, facilitating removal of the formed polymer from the tubing.

If a filament as described herein is wrapped around a mandrel prior to polymerization of the polymerization solution, the resulting polymer will maintain the shape of the filament around the mandrel or at least retain a memory of the shape. Using this technique, helical, tornado, and complex shapes can be imparted to the hydrogel filament. When the tubing is wrapped around a mandrel, trapezoidal and/or oval tubing can be used. After wrapping around the mandrel, the oval shape of the tubing is rounded and the resulting filament has a round shape.

If HYTREL® tubing is utilized, the filament can be recovered by incubating the tubing in a solution of 25% w/w phenol in chloroform followed by washing in chloroform and ethanol. After the filament has been washed, it is dried, and a dried hydrogel filament is produced. The length of a dried filament can range from about 0.01 cm to about 1,000 cm, about 0.1 cm to about 500 cm, about 0.25 cm to about 250 cm, or about 0.5 cm to about 100 cm. The diameter of a filament can range from about 0.01 inches to about 0.1 inches, about 0.001 inches to about 0.01 inches, or about 0.006 inches to about 0.075 inches. In one embodiment the filament has a diameter less than about 0.05 inches, 0.04 inches, or 0.031 inches.

In some embodiments, the polymer described herein can expand initially, before second crosslinker cleavage to about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, at most about 50%, at most about 40%, or between about 10% and about 50% of the polymers full expansion diameter. Then, after cleavage of the second crosslinker, the polymer described herein can expand to about 50%, about 60%, about 70%, about 80%, about 90%, 100%, at least about 50%, at least about 60%, or between about 50% and 100% of the polymers full expansion diameter.

In some embodiments, the polymers described can be incubated in a low pH or high pH solution to protonate or depronate the pH sensitive monomer incorporated into the polymer as necessary rendering it environmentally responsive. The environmentally responsive polymer can expand to a particular dimension after being subjected to a particular pH environment. However, the cleavable crosslinker can prevent the polymer from expanding to its full expansion parameters until the cleavable crosslinkers have been broken and the polymer is allowed to folly expand.

In some embodiments, the second cleavable crosslinker can add about 60 sec, about 1 min, about 5 min, about 10 min, about 15, min, about 20 min, at least about 1 min, at least about 5 min, or at least about 15 min of time before the polymer is fully expanded.

Example 1 Implantation of a Polymer Filament with a Secondary Expansion Mechanism

A patient is implanted with a polymer filament which is crosslinked with a non-degradable crosslinker and a cleavable crosslinker and a pH sensitive monomer. The polymer filament had been treated in an acidic pH solution and dried to render the filament environmentally responsive.

The filament is delivered through a microcatheter to a vessel occlusion. The filament expands in response to the change in pH. After about 10 min, the filament is 50% expanded. After about 15 min, the filament is about 60% expanded. At about 20 min, the cleavable corsslinking bonds begin to break and after 25 min, the filament is about 95% expanded.

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

The terms “a,” “an,” “the” and similar referents used in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

Certain embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

In closing, it is to be understood that the embodiments of the invention disclosed herein are illustrative of the principles of the present invention. Other modifications that may be employed are within the scope of the invention. Thus, by way of example, but not of limitation, alternative configurations of the present invention may be utilized in accordance with the teachings herein. Accordingly, the present invention is not limited to that precisely as shown and described. 

I claim:
 1. A method of forming an expansile polymer, comprising: polymerizing a polymer from a polymerization solution comprising a macromer, a monomer, a first crosslinker, and a second cleavable crosslinker, and treating said polymer in a non-physiological pH for a predetermined amount of time thereby creating an environmentally responsive hydrogel, wherein the expansile polymer has a full expansion size that includes a primary expansion and a secondary expansion, wherein the secondary expansion is retarded by the second cleavable crosslinker.
 2. The method of claim 1, wherein the expansile polymer includes no support members.
 3. The method of claim 1, further including at least one visualization element.
 4. The method of claim 3, wherein the at least one visualization element is selected from metallic powders, gadolinium, superparamagnetic iron oxide particles, or a combination thereof.
 5. The method of claim 3, wherein the at least one visualization element is barium sulfate.
 6. The method of claim 1, wherein the monomer is pH sensitive and provides the primary expansion to the expansile polymer.
 7. The method of claim 1, wherein the second cleavable crosslinker is an acrylate based crosslinker.
 8. The method of claim 7, wherein the acrylate based crosslinker is an acrylic anhydride based crosslinker.
 9. The method of claim 8, wherein the acrylic anhydride based crosslinker has a structure

wherein n is 0, 1, 2, 3, 4, or
 5. 10. The method of claim 8, wherein the acrylic anhydride based crosslinker is synthesized by reaction of a di-acid with methacrylic anhydride.
 11. The method of claim 1, wherein the macromer is poly(tetramethylene oxide).
 12. The method of claim 1, wherein the non-physiological pH is acidic.
 13. The method of claim 1, wherein the non-physiological pH is basic.
 14. The method of claim 3, wherein the at least one visualization element is a metallic powder, gadolinium, superparamagnetic iron oxide particles, barium sulfate, or a combination thereof.
 15. The method of claim 14, wherein the second cleavable crosslinker is an acrylic anhydride based crosslinker.
 16. The method of claim 15, wherein the acrylic anhydride based crosslinker has a structure

wherein n is 0, 1, 2, 3, 4, or
 5. 17. The method of claim 15, wherein the acrylic anhydride based crosslinker is synthesized by reaction of a di-acid with methacrylic anhydride.
 18. The method of claim 1, wherein the first crosslinker is N,N′-methylenebisacrylamide.
 19. The method of claim 1, wherein the expansile polymer has a dry bending resistance to wet bending resistance ratio of about 200:50 to about 20:2, a dry bending resistance of about 20 mg to about 200 mg, and a wet bending resistance of about 2 mg to about 50 mg.
 20. An expansile polymer formed according to the method of claim
 1. 21. A method of forming an expansile polymer, comprising: treating a polymer in a non-physiological pH for a predetermined amount of time thereby creating an environmentally responsive hydrogel, wherein the expansile polymer includes a reaction product of a polymerization solution comprising a macromer, a monomer, a first crosslinker, and a second cleavable crosslinker, and wherein the expansile polymer has a full expansion size that includes a primary expansion and a secondary expansion, wherein the secondary expansion is retarded by the second cleavable crosslinker. 